JPS59157846A - Magnetic disk - Google Patents

Abstract

PURPOSE:To obtain a high output by using needlelike cobalt-contg. iron oxide magnetic powder having triaxial anisotropy as magnetic powder for forming a magnetic layer on a base body and orienting the same in a horizontal direction. CONSTITUTION:A compsn. composed of 270pts. (wt.) gamma-Fe2O3 needlelike magnetic powder dissolving Co as solid solution (5.0wt% content of Co, triaxial anisotropy), 80pts. VAGH (vinyl chloride/vinyl acetate-vinyl alcohol copolymer), 15pts. N1432J (acrylonitrile-butadiene copolymer), 10pts. Coronate L (trifunctional low molecular isocyanate compd.), 34pts. HS-500 (carbon black), 11pts. alpha-Fe2O3 powder, 420pts. methyl isobutyl ketone, and 420pts. toluene is mixed and dispersed for 48hr in a ball mill. Such magnetic coating is applied on both surfaces of a polyester film and an N-N repulsive magnetic field is applied on the film in its longitudinal direction to orient the magnetic powder in a horizontal direction. The coating is then dried to form a magnetic layer having 3mu thickness and the material is blanked into a disc shape, by which a magnetic disk having a high output is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic disk, and an object thereof is to provide a magnetic disk that has good conversion properties and is suitable for high-density storage.

Among magnetic recording media, those in which magnetic recording is performed in the longitudinal direction, such as magnetic tape, have improved electromagnetic conversion characteristics by orienting acicular magnetic powder in the magnetic layer in the longitudinal direction.

In general, a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components is applied onto a substrate such as a polyester film, dried to form a magnetic layer, and then punched out in a circular shape. Since magnetic recording is performed in the circumferential direction of magnetic disks manufactured by lithography, it is not possible to orient the uniaxially anisotropic acicular magnetic powder in the longitudinal direction of the substrate, which is commonly used in the past, as in magnetic tapes. Electromagnetic conversion characteristics cannot be obtained.

For this reason, in conventional magnetic disks, when applying magnetic paint onto the substrate, it is necessary to prevent shearing force from being applied to the paint as much as possible, or to dry it without completely aligning the magnetic field. The uniaxially anisotropic acicular magnetic powder contained in the magnetic tape has been made non-oriented, but when the uniaxially anisotropic acicular magnetic powder is made non-oriented in this way, it becomes difficult to use magnetic tape, etc. It is undeniable that the electromagnetic conversion characteristics will deteriorate compared to the case where the magnetic tape is oriented in the longitudinal direction and direction. No material capable of density recording has been obtained.

The inventors conducted various studies on the magnetic powder to be used in light of the current situation, and used acicular cobalt-containing iron oxide magnetic powder with triaxial anisotropy instead of the conventional uniaxial anisotropic acicular magnetic powder. As a result, it was found that this type of magnetic powder has an isotropic direction of easy magnetization, which increases the output and improves the recording density when used in magnetic disks.After further investigation, it was found that the direction of easy magnetization is isotropic. The acicular cobalt-containing iron oxide magnetic powder with triaxial anisotropy is contained in the magnetic layer in a non-oriented manner.However, this acicular cobalt-containing iron oxide magnetic powder with triaxial anisotropy is still insufficient. When oriented in the horizontal direction and incorporated into the magnetic layer, this type of magnetic powder has an acicular shape, which improves the filling properties and also improves the surface smoothness, further improving the electromagnetic characteristics. It was discovered that a magnetic disk capable of obtaining high output and suitable for high-density recording could be obtained, and this invention was made.

The cobalt-containing iron oxide magnetic powder used in this invention has an acicular shape with an axial ratio of 3.0 or more and a major axis diameter of 0.1 to 0.5μ, in which cobalt is solidly dissolved inside the iron oxide magnetic powder. It is preferable to use a magnetic powder having a triaxial anisotropy of 0.5 μm. If it is granular or has a long axis diameter larger than 0.5μ, the filling property will not be sufficiently improved, and the surface density of the magnetic layer will increase. The thermal properties are also not sufficiently good. In addition, the content of cobalt contained in the iron oxide magnetic powder is 2 to 15% by weight based on the total amount of magnetic powder.
The content is preferably within the range of .

In this way, the acicular magnetic powder with triaxial anisotropy, which contains cobalt as a solid solution inside the iron oxide magnetic powder, is mixed with a binder resin,
A magnetic paint is prepared by mixing and dispersing it with an organic solvent and other necessary components, and this is applied onto a substrate such as a polyester film by any means such as gravure coating or a roll coater, and N-N opposing magnets are used. When the magnetic powder is oriented in the horizontal direction and dried, the magnetic powder contained in the magnetic layer is acicular, so the filling properties of the magnetic powder are high (this results in a magnetic layer with good surface smoothness). In addition, this type of magnetic powder has triaxial anisotropy and isotropically large residual magnetic flux density, so good magnetic recording can be performed in any direction. If a magnetic layer is formed and then punched out into a circular shape to form a magnetic disk, good magnetic recording can be performed in the circumferential direction, and the magnetic powder is contained at a high packing density, resulting in good surface smoothness of the magnetic layer. , a magnetic disk with even higher output and suitable for high-density recording can be obtained.

In order to obtain such an effect, the degree of orientation of the cobalt-containing iron oxide magnetic powder, which is acicular and has triaxial anisotropy and is contained in the magnetic layer, is determined by the Meussbauer method, that is, as shown in Figure 1. A T-ray is irradiated from the direction indicated by the arrow A of the magnetic recording medium 1 stacked on the magnetic recording medium 1 to obtain a spectrum as shown in FIG. 2, and the average intensity of the second and fifth peaks C from the left of this spectrum is , the measured value expressed as the ratio of the average intensity of the first and sixth peaks C from the left (C2,5/C+, 6) is preferably 0.6 or more, and this value is smaller than 0.6. The magnetic powder becomes non-oriented, and the filling properties and surface smoothness of the magnetic layer are not sufficiently improved, making it impossible to obtain high output. Such orientation of the cobalt-containing iron oxide magnetic powder, which is acicular and has triaxial anisotropy and is contained in the magnetic layer, is performed by mechanical orientation by shearing force during application of the magnetic paint and by magnetic field orientation. Mechanical orientation depends on the viscosity of the magnetic paint, and if the viscosity of the magnetic paint is less than 50 centipoise (shear rate 2 x 104 sec'), the shearing force applied to the magnetic paint during application of the magnetic paint is insufficient and the magnetic powder is not sufficiently oriented. Therefore, it is preferable that the viscosity of the magnetic paint is 50 centipoise (shear rate 2 x 10' 5ec-1) or more. More than 50% of the magnetic powder is mechanically oriented by shearing force during application.

As the binder resin used here, conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, polyurethane resins, cellulose resins, and isocyanate compounds are widely used.

Further, as the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethyl formamide, etc. are used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

Next, embodiments of the invention will be described.

Example I Co-solidified r-Fe203 magnetic powder 270 parts by weight (triaxial anisotropy, particle size (major axis) 0.3 μ, axial ratio 10, coercive force 675' Oersted, saturation magnetization 72 emu 7 g, angle Type 0.74, cobalt content 5.
0% by weight) VAGH (manufactured by J, C, C, USA, 80 vinyl chloride-vinyl acetate-vinyl alcohol copolymer) N1432J (manufactured by Nippon Zeon Co., Ltd. 15, acrylonitrile-butadiene copolymer) Coronat Shiku Nippon Polyurethane 10〃Tan Kogyo Co., Ltd., trifunctional small molecular weight isocyanate compound) N3-500 (Asahi Carbon Co., Ltd. 34〃Manufactured, carbon black) α-Fe203 powder 11〃Methyl isobutyl ketone 420〃Toluene
420 This composition was mixed and dispersed in a ball mill for 48 hours to prepare a magnetic paint. The viscosity of magnetic paint is 80
It was centiboise. This magnetic paint was applied to both sides of a polyester film with a thickness of 75 μm, and an N'-, N repulsive magnetic field was applied in the longitudinal direction of the film for magnetic field orientation, and dried to form a magnetic layer with a dry thickness of 3 μm.

Afterwards, it was punched out into a disk shape to create a magnetic disk.

Example 2 In the composition of the magnetic paint in Example 1, the particle size (major axis) is 0.3 μ, the axial ratio is 10, the coercive force is 675 oersted, the saturation magnetization is 72 emu 7 g, the square shape is 0.74, and the cobalt content is 5.0. wt% triaxial anisotropic Co solid solution-Fe2
Particle size (major axis > 0.32μ, axial ratio 10, coercive force 1050 oersted, saturation magnetization amount 73e) in place of 03 magnetic powder
A magnetic disk was produced in the same manner as in Example 1, except that the same amount of triaxially anisotropic Co-solid γ-Fe203 magnetic powder having a square shape of 0.73 g and a cobalt content of 9.5% by weight was used. Ta. The viscosity of the magnetic paint was 75 centipoise.

Comparative Example 1 In the composition of the magnetic paint in the example process, Co solid solution r
-Instead of Fe203 magnetic powder, particle size (long axis) 0.3μ
, axial ratio 0, coercive force 620 oersted, saturation magnetization 7
6 emu 7g, square shape 0.50, cobalt content 5
．． The same amount of 0% by weight uniaxially anisotropic Co-coated Fe203 magnetic powder was used, the amount of methyl isobutyl ketone was changed from 420 parts by weight to 600 parts by weight, and the amount of toluene was changed to 420 parts by weight. A magnetic disk was produced in the same manner as in Example 1 except that the amount was changed to 600 parts by weight and the magnetic field orientation treatment in Example 1 was omitted. The viscosity of the magnetic paint was 20 centivoise.

Comparative Example 2 In the composition of the magnetic paint in Comparative Example 1, instead of the -axis anisotropic CO-coated r-Fe203 magnetic powder, a particle size (major axis) of 0.1 μ, an axial ratio of 8, and a coercive force of 1380 L were used. A magnetic disk was produced in the same manner as in Comparative Example 1, except that the same amount of stained, saturation magnetization 123 emu 7 g, square shape 0.49 uniaxially anisotropic α-Fe magnetic powder was used. The viscosity of the magnetic paint was 25 centivoise.

Comparative Example 3 A magnetic disk was manufactured in the same manner as in Example 1 except that the magnetic field orientation treatment was omitted.

The viscosity of the magnetic paint was 80 centipoise.

Comparative Example 4 A magnetic disk was produced in the same manner as in Example 2, except that the magnetic field orientation treatment was omitted.

The viscosity of the magnetic paint was 75 centipoise.

For the magnetic disks obtained in each example and each comparative example, the coercive force, residual magnetic flux density, squareness, squareness ratio OR1 surface roughness in the coating direction and the direction perpendicular to it were SP values (the larger the value, the smoother the surface roughness). (large pacing) was measured, and the degree of orientation was measured by the Meuss-Bower method. Also, the recording wavelength is 0.83
The C/N at μ was measured.

The table below shows the results.

As is clear from the above table, the magnetic disk obtained in Example 1 has a higher residual debt density than the magnetic disks obtained in Comparative Examples 1 and 3, and has a higher squareness-orientation degree and C/N.
is high and the surface quality is also much improved, and Example 2
Compared to the magnetic disks obtained in Comparative Examples 2 and 4, the magnetic disks obtained in Comparative Examples 2 and 4 had a higher square shape, higher degree of orientation, and higher C/N, and had better surface properties. It can be seen that the surface smoothness of the magnetic layer of the disk is good, and the magnetic properties and electromagnetic conversion properties are improved.

Furthermore, for the magnetic disks obtained in Example 1 and Comparative Examples 1 and 3, the relationship between recording density and output was investigated. Third
The figure shows this relationship in a graph. Graph A is the magnetic disk obtained in Example 1, graph B is the magnetic disk obtained in Comparative Example 1, and graph C is the magnetic disk obtained in Comparative Example 3. This shows the relationship between each. As is clear from these graphs, the magnetic disk obtained in Example 1 (Graph A) is the same as the magnetic disk obtained in Comparative Example 1 (Graph B) and the magnetic disk obtained in Comparative Example 3 (Graph C). Compared to this, the recording density when the output is high and the output is reduced by 50% compared to the low-frequency output is 12 KBPl in Comparative Example 1, 2'OKB in Comparative Example 3, It can be seen that the recording density is 23 KBPI, whereas that obtained in Example 1 is 23 KBPI, which further improves the recording density.

Furthermore, regarding the magnetic disks obtained in Example 2 and Comparative Examples 2 and 4, the recording wavelength was 1.25μ, and the trunk width was 58μ.
When a reproduced output envelope photograph was taken and illustrated when a Mn--Zn ferrite head was used with .mu., an envelope curve as shown in FIG. 4 was obtained. In FIG. 4, curve A shows the envelope curve of the magnetic disk obtained in Example 2, and curve B shows the envelope curve of the magnetic disk obtained in Comparative Example 2. Curve C shows the envelope curve of the magnetic disk obtained in Comparative Example 4, and as is clear from these envelope curves, the one obtained in Example 2 is comparable to that obtained in Comparative Examples 2 and 4. The shape of the envelope curve is good and the output is large, which indicates that the magnetic disk obtained by the present invention can provide high output.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a method for measuring the orientation degree of magnetic powder particles by the Meuss-Bauer method, Fig. 2 is a diagram showing a spectrum obtained by measuring by the Meuss-Bauer method, and Fig. 3 is a magnetic disk obtained by the present invention. FIG. 4 is an envelope curve diagram of the magnetic disk obtained by the present invention and the conventional magnetic disk. Figure 1 ↑ Figure 2 Figure 3 1 2 5 . 10122023 recording density (KBPI)

Claims (1)

[Claims] 1. A needle-shaped cobalt-containing iron gun 4 with triaxial anisotropy was also loaded with powder and oriented in the horizontal direction on the substrate.
A magnetic disk made by forming a magnetic layer and punching it into a circular shape.